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NEWTON’S 2ND Law Unit =
7 &
possibly 11 Dr. John P.=
Cise,
Professor of Physics, Austin Com. College,
1212 Rio Grande St., Austin Tx 78701 jpcise@austincc.edu & The New York Times October 2=
1,
2009 by Jonathan Abrams=
If you use this application of phys=
ics
from The New York Times please inform me by e-mail how you used it. Thanks! DR Cise
Football Players Are Pushing a Different Kind of S=
led
=
span>
Caleb Campbell, a
safety from Army who was drafted by the Detroit Lions last year, was asked =
to
try out for the U.S. Olympic bobsled team.
LAKE PLACID, N.Y. — Caleb Campbell received curious glances =
and
furrowed eyebrows — just like other athletes before him. He is the la=
test
in the lineage of football players turned bobsledders. Skip to next paragraphThe Detroit Lions selected Campbell, a safety from =
Army,
in the seventh round of last year’s college draft. As the N.F.L. season drew near, the Lions received a letter from the Army stating t=
hat
its professional athlete policy had been revised. It wanted Camp=
bell
to serve a two-year commitment. As
he drove from Detroit back to West Point, Campbell received a call fro=
m the
assistant United States bobsled coach Bill Tavares, asking him to try out f=
or
the team. Campbell’s only familiarity with the sport came from watchi=
ng
“Cool
Runnings,” a Disney movie loosely based on a Jamaican bobs=
led
team. Football/bobsled synergy
dates back almost 25 years. Brian
Shimer, the United States men’s bobsled coach, played foot=
ball
at Morehead State and piloted a sled with the former Heisman Trophy winner =
Herschel Walker in the 1992 Winter Olymp=
ics. Willie Gault, a wide receiver who played=
in
the N.F.L. for 11 seasons, was on the team at the Olympic Games four years
earlier. Nearly all
converted football players are bobsled pushers, who thrust the s=
led
down the hill as fast as they can at the start of the race before hopping i=
n. Their frames are nearly uniform — around 6 feet 2, 220 pounds=
. “We’re heavier gu=
ys,
explosive and strong,” said Jesse Beckom III, a fo=
rmer
Iowa State linebacker.=
“Moving a 400-pound sled across the ice, you ne=
ed
some powerful, fast guys.
|
|
INTRODUCTION: F=
our pushers
at 220 lb each push a 400 lb toboggan from rest and reach 25 mph in 112 ft.
The coefficient=
of
kinetic friction between toboggan skids and icy track is 0.017. =
QUESTIONS:=
(a)
Find mass of the toboggan? (b) Find acceleration (ft/s2) of =
the
sled from rest up to 25 mph in 112 ft? Note: 60 mph =3D 88 ft/s (c) Fin=
d the
force of friction on the sled? (d) Find the force the pushers exerted on
sled to achieve the acceleration in (b)? Hint: Be sure to consider the
negative effect that some friction exists between sled runners and icy
track. EXTRA CREDIT: Solve for the force exerted to achieve the final 25
mph using the WORK-ENERGY Theorem. NOTE: Work due to friction is negative. Work done by t=
he
pushers is positive. ANSWERS: (a) 12.5 slugs =
(b) 6
ft/s2 (c) ~ 6.8 lb. (d) ~ 81.8 lb.
|
|
<=
/span>
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